"Irashaimase!" (ee-ra-shy-ma-seh) is the greeting of welcome you'll hear upon entering most sushi restaurants. Irashaimase, indeed, to the world of modern Western sushi, a world in which you can find sushi restaurants in malls and airports and snatch grab-and-go bento boxes from the local supermarket.

As people try to eat more nutritiously and add fish rich in omega-3 to their diets, sushi continues to grow in popularity. The compact little rolls certainly look nutritious - rice, fish, veggies - but how healthy is it to eat sushi?

Sushi for beginners

The Japanese have eaten sushi for centuries, but the sushi we know today originated as a fast-food option in Edo, Japan, in the mid-19th century. People could eat it with their hands or carry it with them as they went to the theatre. Visit a sushi cart or restaurant today, and you'll see two main kinds of rolls - nigiri and maki. Nigiri consists of a mound of vinegared rice topped with a dab of hot horseradish wasabi and a slab of fish, crab, egg, or other topping. A small, thin bamboo mat is used to roll maki, a cylinder of rice wrapped in nori seaweed with a morsel of fish or other filling in the middle.

The health benefits of sushi

Sushi comes in such a staggering variety that many menus offer a pictorial glossary to help you order. Because of this diversity, the nutritional value of one roll to the next can vary. In general, fish provides a lean source of low-calorie, high quality protein. It's also low in saturated fats and cholesterol, making it a heart-healthy food choice. Salmon is especially high in omega-3 fatty acids, which are linked to improved cholesterol levels, lowered blood pressure, and decreased risk of abnormal heart rhythms. Mackerel, lake trout, herring, and tuna also have omega oomph.

The thin sheets of seaweed, or nori, which are flattened, cut, and wrapped around maki and hand rolls, contain mighty minerals. Iodine, essential for proper hormone function, is abundant in this dried sea vegetable. You'll also get the benefit of magnesium, calcium, iron, and antioxidant phytonutrients and folic acid from eating rolls wrapped in nori.

The health risks of sushi

Consider these risks as you peruse that multi-coloured sushi menu:

Covert calories: Since sushi ingredients get rolled up into such tiny packages, it's easy to think you're eating a tiny amount of calories and fat. One plain tuna roll can have less than 200 calories, but add in embellishments like mayonnaise, fried tempura bits, or cream cheese, and you've got yourself one concentrated bundle of fat and calories. Eat one crunchy shrimp tempura roll, for instance, and you're gobbling over 500 calories and 20 g of fat! Both soy sauce and wasabi are low-calorie condiments, but soy sauce can send sodium levels soaring.

Foodborne illnesses: Eating uncooked fish can expose you to bacteria, viruses, and parasites. Roundworm, for example, is a threadlike parasite that can burrow into the stomach and cause painful symptoms that mimic appendicitis. Some kinds of sushi rolls include uncooked fish, but safe and reputable chefs use only fish that has been frozen. The deep freeze will kill off parasites, rendering the fish safer to consume. However, deep freezing will not kill bacteria  it will only stop or slow down its growth until the temperature warms up again. Eating raw fish inherently comes with an increased risk of foodborne illness compared to eating cooked fish.

Mercury levels: The open waters of rivers, lakes, and the sea expose fish to mercury, a known neurotoxin. When we, in turn, eat those fish, some of the mercury transfers to our bodies. Large, predatory fish tend to have the highest mercury levels. This includes the fresh and frozen tuna commonly found in sushi, as well as swordfish, marlin, and shark. Young children, pregnant women, and women planning to get pregnant are advised to minimize their consumption of these fish. Overall, Health Canada advises that the health benefits of fish outweigh the risks of mercury exposure.

Tips for safely savouring sushi

Leave it to the pros. Sushi chefs, or itamae (ita-meh-ee), are highly trained to handle uncooked fish. If you're not an itamae, and you decide to make your own sushi, you could run the risk of parasitic or bacterial contamination. Most home freezers can't reach the low temperature necessary to properly freeze raw fish. Still feeling the urge to make your own rolls? Opt for veggie sushi or use fully cooked fish or crabmeat.

Make it a treat. Think of sushi as an occasional indulgence, rather than a staple meal in your diet. Remember that fried items like tempura or creamy condiments like mayonnaise can have you drowning in calories and fat. Keep these to a minimum.

Take it easy with the tuna. Sure, you love those maguro and toro rolls. But to minimize your risks of mercury exposure, remember: there are other fish in the sea! Eat fish lower on the food chain - the smaller the fish, the less mercury it will have accumulated. Also, wild salmon has less mercury than tuna, as do shrimp, pollock, and catfish.

Veg out. You know, tofu is a potentially good source of omega-3, too. Balance out your sushi feast and fill up on rolls made with yummy, nutritious vegetables - shiitake mushrooms, avocado, and cucumber are standard menu items at most sushi restaurants.